To be honest my audi and my astra both have 18's on with non run flats. Yes the run flats on the 19's are harder. But wheel size isn't much different then the 18s I find. However that's subjective, and someone else may think different.
If you can get them with non runflats great. Would you then get tyre foam? Hardly any tyre places I know will change a tyre with tyre foam in, I've asked about 6.